Weed Management Considerations in Alternative Tillage Systems Fabián Menalled Cropland Weed Specialist 719 Leon Johnson Hall Montana State University

Advantages of No-Till Systems Soil erosion Soil moisture Crop yield Economic returns

Approximately 20-30% of input costs

“The success of conservation tillage in the NGP depends on the development of agronomicallly and economically viable weed management systems” Derksen et al., 1996

Issues to Consider (Related to Weed Management) Weed biology Seed & seedling fate Management considerations Herbicide resistance Weed shifts Herbicide persistence and crop damage

Tillage and Seed Distribution Soil Depth (inch) % 25% 38% Plowed 61% 23% 16% Chisel 74% 9% 18% No-Till After Swanton et al., 2000

Depth and Seed Fate Depth (inch)DormancyGerminationMortality LowHighMedium * MediumLow HighVery LowLow * Mortality of small seeds is usually high at the surface

Harpalus pensylvanicus

Gryllus pennsylvanicus

Peromyscus maniculatus Photo courtesy of P. Westerman

Tillage and Seedbank Dynamics Location: Arthur Post Research Farm Seedbanks Field Pennycress (Thlaspi arvense) Green Foxtail (Setaria viridis) Wild Oat (Avena fatua) Kochia (Kochia scoparia) Seed densities: 800, 1600, 3200, 6400 seeds/m2 Burial depths: surface, top 10 centimeters

2. Spring 2005 Greenhouse germination 3. Separate seeds 4. Test for germination and viability 5. Fall 2005 Repeat with remaining samples Spring 2006 Fall Seedling emergence

Foxtail Density P=0.003 Depth x crop P=0.0041

Pennycress Density x crop P=

Kochia Depth P<0.001 Density P=

Wild Oat Depth P<0.001 Density P=0.015 Depth x crop P=0.004

Time of Emergence % emergence Surface

Questions, so far?

Issues to Consider (Related to Weed Management) Weed biology Seed & seedling fate Management considerations Herbicide resistance

fallowwheatfallowwheatfallowwheat Grassy Weeds

Crop Rotation “Rotation of crops, when accompanied by care in the use of pure seed, is the most effective means yet devised for keeping land free of weeds.” Leighty (1938)

Tillage and Crop Rotation “Changing tillage practices without increasing crop diversity…has generally led to increased weed problems, especially if monoculture is practice” Derksen et al., 2002

Blackshaw et al., 2005 Crop Rotation and Weeds Seed date = April or May Seed rate = 100 or 150% Fertilizer timing = fall or spring Herbicide = 50% or 100% 4 years / 2 sites

Wild oat Common lambsquarters Redroot pigweed Wild buckwheat

Seeding Date No effect on yield After Blackshaw et al., 2005

Seeding Rate Sometimes higher yield in 150% seed rate After Blackshaw et al., 2005

Fertilizer Timing No large effect in yield After Blackshaw et al., 2005

Herbicide Dose No large effect in yield (especially in high seeding rate) After Blackshaw et al., 2005

Conclusions Weed biomass, weed seedbank, and crop yield Similar between 50% and 100% in-crop herbicide Combined use of early seeding rate, higher crop seed, and spring-applied fertlizer Competitive stand Productive crop After Blackshaw et al., 2005

Questions, so far?

Issues to Consider (Related to Weed Management) Weed biology Seed & seedling fate Management considerations Herbicide resistance

Approximately 20-30% of input costs

Herbicide Resistance is NOT due to: 1.Sprayer skips or plugged nozzles 2.Weather problems that cause poor control 3. Plants that are ‘naturally tolerant’ to the herbicide 4. Genetic changes caused by the herbicide

Herbicide Resistance is: The ability of a plant to survive and reproduce after treatment with a dose of herbicide that would normally kill the plant Banvel-resistant kochia

Susceptible Resistant

Where do Resistant Weeds Come From? One in one million, billion, trillion….? It’s all about selection…..

DNA Resistance passed on to next generation Herbicide application: selection pressure for resistant plants Succeeding generations are also resistant Herbicide application: selection pressure Reproduction (sets seeds) DNA mutation: allows resistance to a herbicide

Wild Oat, Herbicide Resistance Beginning of Time1970Fargo 1990Resistance to Fargo Cross Resistance to Avenge Early 1990s Assert 1996Resistance to Assert Multiple resistance Fargo, Avenge & Assert 2004 Resistance to Discover

WeedSituationHerbicide Mode of Action Kochiarailways Photosystem II inhibitors (atrazine) wheat ALS inhibitors (chlorsulfuron, metsulfuron-methyl) wheat Synthetic Auxins (dicamba, fluroxypyr) Wild oatbarley Thiocarbamates and others (difenzoquat, triallate) barley Pyrazoliums (difenzoquat, triallate) sugarbeet, wheat ACCase inhibitors (diclofop-methyl, fenoxaprop-p-ethyl, tralkoxydim) cereals ALS inhibitors (imazamethabenz-methyl) Russian Thistlewheat ALS inhibitors (chlorsulfuron) Persian Darnellwheat ACCase inhibitors (diclofop-methyl)

Herbicide Resistance  Idaho Prickly lettuce Kochia Russian thistle Wild Oat Italian ryegrass Mayweed chamomile  Wyoming Kochia Italian ryegrass  North Dakota Kochia Green foxtail Wild oat Redroot pigweed Wild mustard E. black nightshade  Utah Kochia

Herbicide Resistance (Canada)  Alberta Wild Oat Common hempnettle False cleavers Kochia Ball mustard Green foxtail Spiny sowthistle Common chickweed Field pennycress  Saskatchewan Kochia Green foxtail Wild oat Russian thistle

Herbicide Resistance  Selection intensity Herbicide efficacy Length of soil residual period Number of herbicide applications / year

Selection Pressure is Affected by: Herbicide Quality “Better” herbicide = more chance of resistance

Herbicide Resistance  Selection intensity Herbicide efficacy Number of herbicide applications / year  Genetics of resistance ALS or ACCase vs. EPSP synthase  Weed biology Genetic variability Reproduction mechanism

Resistance Management Keep selection pressure low Rotate herbicide families Use non-herbicide control measures Use tankmixes (?) Rotate crops

To Till or Not to Till?

Questions?